4457 - depth of field is too shallow; the saucer is in focus while the cup's rim is not.
1838 - focus appears to be too soft and the foreground is underexposed
3533 - underexposed shadows, overexposed sky
3504 - underexposed, soft focus; I've found that it's difficult to get any "misty" images like this accepted, because the Moderators just see the mist as "soft focus"...
Thanks for the quick response! I looked at the photo differently and now I really see more errors.
It's always important to review your photos on a big screen at 100-200% magnification (this is what the moderators will be doing as well.) When you look at 4457, in truth, nothing is in focus and it is very grainy.
For landscape photos, shallow DOF rarely works out well. For the wide angle shots, I would personally use at least F11. In 1838 the stone wall isn't in focus and the foreground is so blurry that it is distracting. The shadows need to be lifted to balance out the exposure. I would also rotate the image a couple of degrees to level out the stone wall (in the same way that any shot including a horizon needs to be level.) There are a few birds in the sky that just look like black dots because they are so far away, so it would be worthwhile to just clone them out.
In addition to what Jill said regarding 3533, I would also rotate that image so that the tree and the waterfall are vertical. I know it sounds nitpicky, but visually it does make a difference when people look at photos that are slightly askew. They often know that something isn't quite right, but not sure what exactly it is - could be the sloping horizon or waterfall that is flowing slightly sideways. 🙂
As for the photo with the mist, Jill is right again and those are difficult to get accepted. I personally love the moodiness of the mist in the pines, but from personal experience I have only had one similar photo accepted. The only other suggestion I would make is to work on the exposure - the mist up top seems slightly overexposed and the base of the trees underexposed. It's a great subject matter to work on your photography skills and you can get some great artistic photos (but maybe not always the photos that stock photography sites want.)
Best of luck with your future submissions.
Thank you for such a detailed response and support!